Discovery and application of 6π-azaelectrocyclization to natural product synthesis and synthetic biology

A Torquoselective Thermal 6π-Electrocyclization Approach to 1,4-Cyclohexadienes via Solvent-Aided Proton Transfer: Experimental and Theoretical Studies

The thermal 6π-electrocyclization of hexatriene typically delivers 1,3-cyclohexadiene (1,3-CHD). However, there is only limited success in directly synthesizing 1,4-cyclohexadiene (1,4-CHD) using such an approach, probably due to the difficulty in realizing thermally-forbidden 1,3-hydride shift after electrocyclic ring closure. The present study shows that by heating (2E,4E,6E)-hexatrienes bearing ester or ketone substituents at the C1-position in a mixture of toluene/MeOH or EtOH (2 : 1) solvents at 90-100 °C, 1,4-CHDs can be selectively synthesized. This is achieved through a torquoselective disrotatory 6π-electrocyclic ring closure followed by a proton-transfer process. The success of this method depends on the polar protic solvent-assisted intramolecular proton transfer from 1,3-CHD to 1,4-CHD, which has been confirmed by deuterium-labeling experiments. There are no reports to date for such a solvent-assisted isomerization. Density functional theory (DFT) studies have suggested that forming 1,3-CHD and subsequent isomerization is a thermodynamically feasible process, regardless of the functional groups involved. Two possible successive polar solvent-assisted proton-transfer pathways have been identified for isomerization.

Low-energy Ga2O3 polymorphs with low electron effective masses

We predict three Ga₂O₃ polymorphs with P2₁/c or Pnma symmetry. The formation energies of P2₁/c Ga₂O₃, Pnma-I Ga₂O₃, and Pnma-II Ga₂O₃ are 57 meV per atom, 51 meV per atom, and 23 meV per atom higher than that of β-Ga₂O₃, respectively. All the polymorphs are shown to be dynamically and mechanically stable. P2₁/c Ga₂O₃ is a quasi-direct wide band gap semiconductor (3.83 eV), while Pnma-I Ga₂O₃ and Pnma-II Ga₂O₃ are direct wide band gap semiconductors (3.60 eV and 3.70 eV, respectively). Simulated X-ray diffraction patterns are provided for experimental confirmation of the predicted structures. The polymorphs turn out to provide low electron effective masses, which is of great benefit to high-power electronic devices.

The 6π-azaelectrocyclization of azatrienes. Synthetic applications in natural products, bioactive heterocycles, and related fields

Covering: 2006 to 2018 The application of the 6π-azaelectrocyclization of azatrienes as a key strategy for the synthesis of natural products, their analogs and related bioactive or biomedically-relevant compounds (from 2006 to date) is comprehensively reviewed. Details about reaction optimization studies, relevant reaction mechanisms and conditions are also discussed.

Tailoring the electronic structure of β-Ga2O3 by non-metal doping from hybrid density functional theory calculations

Se-doped and I-doped β-Ga₂O₃ are theoretically found to be promising photocatalysts for water splitting in the visible region.